There is an increasing need to find sources of human stem cells, other than fetal tissue, that can be used to regenerate tissues and organs. A source of cell lines that are relatively uncommitted or progenitors (e.g., pluropotent) could provide an enlarged supply of stem cells for use in somatic transplantation or organ regeneration therapies, for examples.
Mouse pluropotent stem cells (mPSC) have been derived from the inner cell mass cells of blastocysts and from primordial germ cells colonizing the developing gonadal ridge and are referred to as embryonic stem (ES) cells and embryonic germ (EG) cells. When mPSCs differentiate in vitro, they form complex three-dimensional cell aggregates termed embryoid bodies (EBs). Some early developmental processes are recapitulated within the environment of an EB, resulting in a haphazard collection of precursor and more fully differentiated cells from a wide variety of lineages. Through this intermediate step, mPSCs can generate cells of the hematopoietic lineage (Wiles and Keller, Development [Cambridge, U.K.], 111:259-267, 1991 Keller et al., Mol. Cell. Biol. 13:473-486, 1993), cardiomyocytes (Klub et al., Am. J. Physiol. 269:H1913-H1921, 1995 Rohwedel et al., Cell. Biol. Int. 20:579-587, 1996), neurons (Bain et al., Dev. Biol. 168:342-357, 1995) and glial precursors (Brustle et al., Science 285:754-756, 1999), skeletal muscle (Rohwedel et al., Dev. Biol. 164:87-101, 1994), vascular endothelial cells (Wang et al., Development [Cambridge, U.K.] 114:303-316, 1992), visceral endoderm (Abe et al., Exp. Cell Res. 229:27-34, 1996; Doetschman et al., J. Embryol. Exp. Morphol. 87:27-45, 1996) and glucose-responsive insulin producing cells (Soria et al., Diabetes 49:157-162, 2000). ES cells and EG cells differ phenotypically with respect to their culture requirements and cell surface markers, probably the result of their derivation and tissue source. ES and EG cells propagated in vitro can contribute efficiently to the formation of chimeras, including germlike chimeras.
When human EG cells differentiate, they also form EBs comprised of endodermal, ectodermal, and mesodermal derivatives (Shamblott et al., Proc. Natl. Acad. Sci. USA 95:13726-13732, 1998).
For a review of pluripotent stem cells, including discussions of assay methods, differentiation in vitro, and in vivo applications, see, e.g., Shamblott et al., “Pluripotent Stem Cells,” in Principles of Tissue Engineering (2nd ed.), Academic Press, 2000, pp. 369-381.